Field of the Invention
The invention relates to a power regulating technology, and more particularly, to a timing generator and a timing generation method for a power converter.
Description of Related Art
A DC-DC power supply design nowadays usually adopts a constant on time (COT) architecture. FIG. 1 is a schematic diagram of the DC-DC conversion circuit utilizing a conventional constant on time architecture. A comparator 110 compares an error signal Err with a ramp signal RAMP to generate a compared signal CM. A timing control circuit 120 provides a pulse width modulation signal PWM according a constant on time mechanism and the compared signal CM, in which a width of an On-time Ton is related to an input voltage Vin and an output voltage Vout.
FIG. 2 is waveform schematic diagram of the power converter 100. Please refer to FIG. 1 and FIG. 2 together. The error signal Err and the ramp signal RAMP are utilized to determine when to output a turn-on time Ton signal, in which a size of the error signal Err is related to both a feedback signal Vfb and a reference voltage Vref. While outputting the turn-on time Ton signal, the timing control circuit 120 starts to calculate a turn-on time signal Xon, and the turn-on time Ton of each period in the turn-on time timing signal Xon is fixed. However, despite that a conventional pulse width modulation operation architecture may achieve a fixed frequency effect, when the output voltage Vout is changed with variation of a load current IL, the timing control circuit 120 is still providing the same energy with the fixed frequency within one period, which results in that a power converter 100 to exhibit a poor performance during a load transient period.
In addition, as similar to the power converter 100 of FIG. 1, the timing control circuit 120 may be changed to adopt an adjustable on time mechanism.
FIG. 3 is a waveform schematic diagram of a conventional adjustable on time mechanism. The conventional adjustable on time mechanism utilizes the error signal Err related to the output voltage as an upper boundary to end a counting signal Cton. During a load transient period, the On-time Ton of the pulse width modulation signal PWM may be changed with the error signal Err. In case when energy of the output voltage Vout is insufficient, the On-time Ton of the pulse width modulation signal PWM may extend continuously.
FIG. 4 is a schematic diagram of comparing waveforms in the conventional constant on time mechanism and the conventional adjustable on time mechanism. Waveforms of the output voltage Vout and the load current Iload in the constant on time mechanism are marked as 410 and 430, respectively. Waveforms of the output voltage Vout and the load current Iload in the adjustable on time mechanism are marked as 420 and 440, respectively, and an ideal waveform of the load current Iload is marked as 450. In view of waveforms comparison in FIG. 4, it can be know that a climbing speed of the load current (waveform 440) of the adjustable on time mechanism is faster than a climbing speed of the load current (waveform 430) of the constant on time mechanism. However, before a closed loop control in the adjustable on time mechanism is stabilized, the output voltage Vout (waveform 420) shows a constantly oscillating. Therefore, both of said conventional technologies cannot help to improve the oscillating problem of the output voltage Vout.